ALSA: es18xx: check control allocation before private data setup

ALSA: es18xx: check control allocation before private data setup

snd_es18xx_mixer() creates controls with snd_ctl_new1() and then stores
bookkeeping pointers or sets private_free before calling snd_ctl_add().
snd_ctl_new1() can return NULL on allocation failure, so those writes
can dereference a NULL control pointer.

Check the returned control pointers before using them and return -ENOMEM
on allocation failure.

Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com>
Link: https://patch.msgid.link/20260607074219.3-1-ruoyuw560@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>